Ultra-rapid landscape response and sediment yield following glacier retreat, Icy Bay, southern Alaska

Glacial retreat and opening of Taan Fjord (an ann of Icy Bay, Alaska) in the last two decades drove a base level fall of similar to 400 m at the outlets of four tributary valleys in the region of the current Tyndall Glacier terminus. Response in the tributary valleys to this base level fall includes evacuation of stored sediment, incision of slot gorges into bedrock, and landsliding on valley walls. Fluvial transfer of eroded bedrock, glacial deposits, and stored nonglacial fluvial deposits after 1983 resulted in progradation of fan deltas toward the fjord centerline at the outlet of each of the four catchments. In the largest nonglacial tributary valley, similar to 0.08 km(3) (-8%) of the 0.59 km(3) of > 500-m-thick stored fluvial and colluvial deposits has been transferred to the adjacent fjord. A percentage of the fjord sedimentation in the last two decades thus includes material eroded from bedrock and stored in the landscape during the previous glacial expansions. Distal deltaic deposits extend across the fjord floor and likely interfinger with distal proglacial deltaic deposits sourced from the Tyndall Glacier. A paraglacial landscape response, such as the one exhibited in upper Taan Fjord where sediment delivery to fjords from tributary sources in synchrony with sediment produced by primary bedrock erosion by glaciers, helps to explain the order-of-magnitude discrepancy between sediment yields from Alaskan tidewater glaciers on 10(0)- to 10(2)-year timescales and sediment yields and exhumation rates on 10(4)- to 10(6)-year timescales. (c) 2006 Elsevier B.V. All rights reserved.